The age composition of the pigtoe populations in Wheeler and 

 Chickamauga Reservoirs was estimated by converting length frequencies 

 to corresponding age frequencies. The age composition of the pigtoe 

 stocks was based on the specimens collected in SCUBA samples, 313 from 

 Wheeler and 212 from Chickamauga. 



Reproduction of the pigtoe . --Samples of pigtoes were collected 

 from Wheeler Reservoir, confined, and examined periodically during the 

 months of April through September of 1957, to determine sexual develop- 

 ment in the females and define the duration of their spawning season. A 

 sample of 100 mussels was collected on each of ik days during the 6-month 

 period. Sexual development was determined by microscopic inspection of 

 the marsupia (brood pouches in gills) of gravid females. Stages of develop- 

 ment were classified as follows: 1. fertilized eggs; 2. immature glochidia 

 (in membrane); 3. free glochidia (out of membrane). The effect of water 

 temperature on sexual development was observed during the spawning season. 

 The age at which female pigtoes started and stopped reproducing was also 

 determined by examining several hundred small and large mussels collected 

 d\iring the spawning season. 



Surber (l915) described the glochidia of the pigtoe mussel based 

 on size dimensions and shape. During the course of the present study, 

 measurements were taken from 100 glochidia selected at random from marsupia 

 to check the dimensions described in Surber 's Key. 



During the spawning seasons of 1956 and 1957, efforts were made to 

 find the natural host- fish which may be necessary for the pigtoe glochidia 

 to survive. Fish collections were made with hoop nets, gill nets, and 

 rotenone. A tota:l of 283 fish composed of 17 species were used in I956 

 and 330 fish composed of I6 species in 1957- Gill filaments were inspected 

 by microscope, and all encysted glochidia foxmd were closely examined to 

 identify them. 



When applicable, standard statistical methods and procedures as 

 described by Snedecor (1956) were used in the analyses of data in this 

 report . 



ANALYSES OF DATA 



Commercial catch. — Catch records from Wheeler Reservoir showed 

 that 6,116 boxloads of mussels were harvested in I956 and 3,108 boxloads 

 in 1957 (table l), a decline of U9.2 percent. On the basis of box-count 

 samples, the mean number of pigtoes per boxload was found to be 653 

 (620 - 688; 95^ confidence intervals). The mean number per box multi- 

 plied by the total boxloads caught each year, resulted in an estimate 

 of 3,995,051+ pigtoes harvested in 1956 and 2,029,521+ harvested in 1957* 

 When converted to a catch per unit of area basis, the harvest amoimted 

 to O.53I4- pigtoes per square yard in I956 and O.27I in 1957 (table 2). 



